Wood-pulping process

ABSTRACT

Woolly wood fibers having lengths in the range of one-sixteenth to one-quarter of an inch and cross-sectional dimensions within the range of 0.1 to 0.05 mm., obtained by grinding wood chips of the order of one inch in length in a ribbed plate grinder, are digested in a continuous type of digester by heating such fibers at a temperature in the range of 220* F. to 330* F. for a period of 1 to 20 minutes in acid bisulfite, bisulfite or neutral sulfite cooking liquor. The consistency of the mixture is controlled by regulating the amount of cooking liquor which is recirculated through the digester, and the consistency of the mixture governs the speed of its flow through the digester and consequently controls the cooking time.

United States Patent [72] Inventors Curt Uschmann Lebanon; ErikBerglund, Oswego, both of Greg. [21] Appl. No. 680,731 [22] Filed Nov.6, 1967 [45] Patented Sept. 21, 1971 [73] Assignee Process DevelopmentCorporation Portland, Oreg.

[54] WO0D-PULPING PROCESS 2 Claims, 1 Drawing Fig.

[52] US. Cl 162/17, 162/24, 162/41, 162/61 [51] Int. Cl D2lb1/04, D21c3/24 [50] Field oiSeorch 162/17, 19, 24, 28,41,71,61,25

[56] References Cited UNITED STATES PATENTS 2,508,043 5/1950 Schaefer162/96 X 2,789,051 4/1957 Obenshain... 162/17 3,192,102 6/1965 Nolan162/24 DIGESTEI? 14s No. 28 pp. 38-41 Rydholm, Pulping Processes pp. 50-52 lnterscience Publishers New York 1965 Primary Examiner-S. LeonBashore Assistant Examiner-Thomas G. Scavone Attorney-Robert W. BeachABSTRACT: Woolly wood fibers having lengths in the range ofone-sixteenth to one-quarter of an inch and cross-sectional dimensionswithin the range of 0.1 to 0.05 mm., obtained by grinding wood chips ofthe orderof one inch in length in a ribbed plate grinder, are digestedin a continuous type of digester by heating such fibers at a temperaturein the range of 220 F. to 330 F. for a period of l to 20 minutes in acidbisulfite, bisulfite or neutral sulfite cooking liquor. The consistencyof the mixture is controlled by regulating the amount of cooking liquorwhich is recirculated through the digester, and the consistency of themixture governs the speed of its flow through the digester andconsequently controls the cooking time.

DRAINER 1J Another object is to provide such a process which iseconomical because it requires a smaller quantity of chemicals thanwould be used in comparable processes and enables cooking of the pulp tobe controlled more easily and accurate ly in a continuous process.

A further object is to digest woolly wood fibers in the production ofpulp which are produced by a procedure which minimizes damage to andweakening of the fibers.

The drawing illustrates diagrammatically equipment which can be utilizedin performing the process of the invention.

Wood chips utilized in the production of pulp according to the presentinvention are of the conventional type used in the production of pulp,being approximately 1 inch in length. Such chips are customarily, thoughnot necessarily, coniferous and may be produced from logs or from woodwaste. For the purpose of this invention, the chips can be produced fromwood waste from lumber mills and other woodworking plants or from forestwaste logs or pulp logs and debris. In the performance of the presentprocess, it is necessary that such chips be treated specially beforebeing defiben'zed, such as being dried, moistened, steamed, soaked ordigested. On the contrary, such chips can be defiberized withoutincreasing or decreasing their natural moisture content. 7

The pulp chips are mechanically defiberized in a ribbed rotary plategrinder. A grinder which is satisfactory for this purpose is shown inUschmann US. Pat. No. 2,776,800. In such a plate grinder the chips arefed between relatively rotating ribbed plates. One plate may be rotatedand the cooperating plate held stationary or two cooperating plates maybe rotated respectively in opposite directions. Most of the fibersresulting from such grinding are one-quarter of an inch or less inlength and have cross-sectional dimensions in the range of 0.1 to 0.05mm. Such fibers have from 20 to 40 times more surface area thansplinters or slivers. Such large surface area greatly increases thecontact area between the cooking liquor and the wood during thesubsequent cooking process and is very important in expediting cookingof the pulp and uniformity of the resulting product.

The defibration of the wood chips by use of a ribbed plate grinder ismuch more desirable than breaking up the chips by use of a hammer millor rod mill because the pounding of such mills flattens and weakens thefibers instead of merely pulling them apart. Consequently, the resultingpulp, after being cooked, is weaker than that produced from woolly woodfiber discharged from a plate grinder.

From the defibrating chip grinder 1 shown in the drawing the resultingwoolly wood fibers, having a length in the range of one-sixteenth of aninch to one-quarter of an inch and a maximum cross-sectional dimensionin the range of 0.1 to 0.05 mm., are fed into the digester 2 through asuitable pressure-retaining feeder 3. This feeder can be of thecompaction feed-screw type, or a dry blower, or rotary feeder, which iscapable of feeding the wood fibers into the digester while it ismaintained under pressure sufficient to keep the temperature of itscontents above the boiling point of water. Alternatively, the woodfibers can be supplied to liquid being fed into the digester so as toform a slurry with such liquid.

Other ingredients fed into the digester 2 are steam through a steamsupply line 4 in sufiicient quantity and at a temperature high enough tomaintain the contents of the digester heated to the proper degree and,through a supply line 5, makeup chemicals to replace chemicals discardedfrom the digester. In addition, cooking liquor is recirculatedcontinuously, being withdrawn through a line 6 from the drainer 7 by apump 8. Such pump forces the recirculating liquor through a controlvalve 9 and a return line 10 into the upper portion of the digester. Aslurry containing cooked pulp and a greater or lesser quantity of wastecooking liquor which has not passed through the drainer screen forrecirculation to the digester is withdrawn from the drainer above itsscreen through the line 1 l.

The cooking liquor used in the digester is of conventional typedepending upon the characteristics of the pulp desired and the purposefor which the pulp is to be used. Such cooking liquor can, for example,be of the acide bisulfite type, as described in US Pat. No. 3,192,102,at column 10, lines 45 to 65 or of the bisulfite type, such as describedin that patent at column 12, lines 30 to 43, or of the neutral sulfitetype, such as described in that patent at column 12, line 74, to columnl3, line 2, and column 13, lines 18 to 21. If the temperature of thecooking liquor within the digester is maintained in the temperaturerange of 220 to 330 F. requiring a pressure within the range of 3p.s.i.g., to p.s.i.g., sufiicient cooking of the wood fibers can beaccomplished within a period of 1 minute to 20 minutes.

The effectiveness of the cooking liquor in the digester can be regulatedby adjusting the proportion of the cooking liquor which is recirculatedthrough the system 6, 8, 9 and 10, as compared to the amount which isdiscarded through line 11 with the cooked wood fibers. The more liquorrecirculated, the more dilute will be the mixture in the digester and,consequently, the faster such mixture will flow through the digester.The speed of flow of the mixture through the digester can thus beregulated to provide the appropriate amount of time to afiord propercooking of the wood fibers. The large surface area of the woolly fibermaterial provides a large surface area for contact of the cooking liquorand reduces the penetration required to cook the wood so that theeffectiveness of the cooking operation is greatly increased over theconventional operation of cooking wood in the form of pulp chips or evenslivers. Moreover, the uniformity of cooking effect on the wood fibersis greatly increased.

The amount of lignin extacted from the wood fibers depends, of course,on the type and concentration of cooking liquor used, the temperature ofthe cooking liquor and the cooking time. For some uses, it is desirableto wash the cooked wood fiber for the purpose of removing from it thewaste cooking liquor carrying the lignin. On the other hand, if theresulting pulp is to be used in the manufacture of fiberboard, forexample, it is not objectionable for the lignin content of the cookingliquor to remain mixed with, although extracted from, the cooked fiber.In such case, instead of washing the waste sulfite liquor from the pulp,the water content can simply be evaporated leaving the lignin behinddeposited on the fiber so that its binding characteristics can beutilized in the production of fiberboard.

As in other types of pulp-making processes, the waste liquor should beburned or should be purified before being discarded to a natural watercourse to avoid water pollution.

I claim:

1. The process of making wood pulp which comprises grinding wood chipsinto woolly fibrous material in which the ground fibers have a length inthe range of one-sixteenth of an inch to one-quarter on an inch andmaximum cross-sectional dimensions in the range of 0.1 to 0.05 mm, andthereafter digesting the woolly wood fibrous material in a pulp-cookingliquor heated to a temperature in the range of 220 to 330 F. selectedfrom the group consisting of acid bisulfite liquor, bisulfite liquor andneutral sulfite liquor for a period within the range-of l to 20 minutesin a continuous process by feeding the woolly fibrous material into adigester, withdrawing the digested pulp and cooking liquor from thedigester without interruption of the digesting process, separating thedigested pulp from the cooking liquor and returning the cooking liquorto the digester.

The whole was passed into an oven at 150 C., and kept there for 1-2minutes. Thereafter, onto the previous layer a second layer (foamed) wasspread. which consisted of:

PVC, paste making resin having a K-value of 72 dioctyl phthalate 100parts (by weight) 80 parts (by weight) The initial thickness of thislayer was 200 microns.

The whole was then passed into an oven at 200 C. and kept there for l-2minutes. The release paper was then removed. The system was thensubjected to a slight tension in order to facilitate the separation ofthose components that were incompatible with each other; then the systemwas coupled to a cotton jersey fabric (with the second layer adjacent tothe fabric), after preliminarily having spread on the fabric someplastisol of the first layer which served as a binder. Said couplingoccurred in about 1 minute in an oven heated to ISO-170 C.

The poromeric material thus obtained showed the following airtranspiration rates:

Pressure (mm. Hg)

The release paper was then removed and the system was subjected to aslight tension and subsequently was coupled to a jersey fabric made ofpolyamide fibers, the second layer being adjacent to the fabric afterpreliminary having spread on the fabric some plastisol of the firstlayer which serves as a binder.

The poromeric material thus obtained shows the following airtranspiration rates:

Pressure cm. of air (mm.Hg) hr. cm.

4U 80 60 121 I00 205 ISO 270 Example 3 100 parts (by weight) PVC, pastemaking resin with a

2. The process defined in claim 1, including controlling the amount ofcooking liquor returned to the digester to regulate the amount ofdilution of the mixture in the digester and consequently to control thetime the mixture remains in the digester.